Differential patterns of genetic exchange via sexual reproduction can have a profound impact on genetic variation and evolutionary divergence within and between populations. This is especially true when the frequency of exchange can vary over several orders of magnitude. Using the androdioecious model nematode, C. elegans, and its dioeceous relative, C. remanei, parallel research projects are proposed to identify or classify the genes underlying differential reproduction among strains and differential fitness between sexes of these organisms. The objectives of this research are to: 1. Map the genes contributing to among strain differences in male frequency and evaluate their function. Preliminary data demonstrates that the frequency of males maintained in C. elegans can differ between strains by as much as factor of 3,000. Using 240 recombinant inbred lines (RIL) that have been genotyped at >1200 single nucleotide polymorphic loci, genomic regions associated with this difference in male mating ability will be identified and functionally assessed using high throughput approaches including the analysis of gene expression, knockdown using interfering RNA (RNAi), and transformation rescue. 2. Determine the nature of the genes underlying sexual conflict and sperm competition in C. remanei, a strictly outcrossing species of Caenorhabditis that is emerging as a model organism for evolutionary ecology research. Preliminary results indicate the presence of sperm competition and sexual conflict within this species. Depending on female and male genetic backgrounds, male mating can reduce female longevity by as much as 33% in a strain specific manner. Crosses among strains divergent for male effects on female longevity and sperm competitive ability will be used to identify the genetic basis of these male mating ability associated traits. Relevance: Understanding the genetic basis of complex traits, including human conditions such as heart disease, obesity, and mental illness known to be influenced by a large number of interacting genes, is one of the major challenges of modern biology. This work serves as a model of how one can utilize high-throughput genomic approaches to understand the molecular genetic basis of complex traits. Further, sex specific effects and interactions are ubiquitous features of all organisms, including humans, and understanding their genetic basis can yield insights into the forces structuring what is certain to be a large fraction of the genome.